1. Field of the Invention
The present invention relates to a method for producing hardened cement mineral material, especially concrete.
In accordance with the proposed method of the present invention, a hydraulically setting binding agent is used, such as portland cement or iron furnace or blast furnace slag, and the binding agent is mixed with water, and when desired, filler material, in order to produce a hardened material.
The invention also concerns an apparatus for hydrating a rapid hardening binding agent used in the production of a cement mineral material, especially concrete or mortar.
2. Description of Related Art
As known in the art, building technology today is based mainly on the use of a material called concrete, while different kinds of mortars and trowelling materials based on the same types of binding agents are in use. Concrete, as well as the abovementioned mortars and trowelling materials, are materials in which stone aggregates and/or sand are bonded together with a binding agent. The reinforcement of these materials is usually based on the use of steel rods or cables.
The aforementioned binding agent is most generally produced by a firing method at a high temperature, where compounds capable of re-reacting with water and recrystallizing into a new compound containing water are formed. The concrete mix or the aforementioned mortar can then be produced by mixing the binding agent and the filler material to be bonded using water, casting, and allowing to set. A defined period of time is required for the hydration and recrystallization process.
Concrete mixes produced of currently available construction cements typically achieve their normal strength in about 28 days.
It has become customary to fabricate structural elements from the aforementioned concrete and steels because the characteristics of said concrete, such as its high pH level resulting from the lime released in the hydration process, protect steel-reinforced parts from corrosion over an extended period of time. During the setting of a typical modern concrete, a relatively high amount of heat is developed in the hydration process and the subsequent crystallization process. Thus, the major portion of heat developed is released during the aforementioned hydration process, and a minor portion released later, during the crystallization process. The strength of the concrete matrix is only developed during the subsequent crystallization process when the crystalline needles grow, initiating from the different particles, progressively approaching each other and finally coalescing.
The production method of concrete in the art is recognized as incorporating the following disdvantages of a fundamental nature:
slow setting, resulting from the necessity of required hydration preceding the crystallization process, PA0 formation of so-called microcracks caused by high internal heat development, PA0 problems caused by high pH, resulting in a relatively small selection of applicable reinforcement materials, PA0 only such reinforcement materials which are tolerant to a high pH or require a high pH, can be used, PA0 so called macro-compactivity is relatively poor in a concrete mix, in which the fine-ground cement, stone and sand aggregates are mixed together with water because water will be used in excess and no "padding" components are present, and PA0 microporosity is created by microcracks which are mainly caused by internal stresses.
Furthermore, today's cement requires strictly defined raw materials. Typical examples of practical limitations associated with the use of limes containing magnesium, are the formation of periclase phase, as well as the swelling and cracking of concrete at a later stage.
As is commonly known in the art, the binding agent particles are hydrated by the effect of water during the preparation of mixes consisting of a binding agent, water, and stone aggregates. Starting from the surface of binding agent particles, the hydration process proceeds by gel formation and therefrom towards elementary crystals, which grow by lengthening and coalescence with the gels of other binding agent particles. Thus, a network of crystals is formed which binds the material. Through this process the material is stiffened, strengthened, and developed to final strength as the crystals grow in size.
In conventional cement and concrete technology, hydration leads to the formation of calcium silicate gel and its subsequent crystallization both of which processes proceed almost simultaneously and immediately follow each other. Today, the conventionally used portland cement is normally ground to a mesh of 325 to 450 m.sup.2 /kg, with the average size of particles being about 25 micrometers. Continued grinding into a finer mesh does not lead to a greater strength of the concrete produced by normal methods from portland cement, and, disregarding the initial stiffening, neither does the development of strength significantly improve. This is caused by the fact that hydration reaches a major portion of the surfaces and even of the cores of cement particles at the aforementioned fineness of mesh of particles. On the other hand, for instance, when the binding agent is produced from ground slag, pozzolanic materials, etc., an essentially finer mesh is required in order to achieve a rapid development of strength because the depth development of gelling is smaller and, consequently, the gelling time is longer.
Modern concrete technology recognizes a great number of admixturing and complementing mixing constituents, which are used in cement and concrete when producing the most suitable concrete mix for particular applications in a particular environment.
Mixing constituents added to cement are fly ash and microsilica, which react in a pozzolanic manner and are readily available from nature in a sufficiently fine mesh allowing their use without grinding. In addition to these, as is generally known, normal portland cement requires about 4 to 8% gypsum as an initial retarder.
Performing as plasticizers, concrete is complemented with organic admixtures, which comprise high molecular weight compounds with an extremely hydrophilic group and an extremely lyophilic group. The lyophilic group attaches the aforementioned molecule of the admixture to the cement particle surface and the hydrophilic group binds water, thus preventing the mutual flocculation of particles. These kinds of molecules operate as spacing constituents between the particles, and thus perform in the capacity of an internal lubricant between the particles. The use of these admixtures reduces the quantity of cement mixing water required, and thereby diminishes the number of pores remaining in the set cement, caused by an excess number of pores resulting from the use of excess water. Examples of these admixtures to be mentioned include high-molecular weight compounds, generally provided with a hydrophilic character by sulfonation, such as the sulfonates of melamine formaldehyde or naphthalene formaldehyde condensate.
In addition to the aforementioned, air entraining admixtures are known in the art, which are typically used for attaining a higher tolerance to frost in concrete surfaces subjected to weathering. The simple effect of the air entraining admixture is to reduce surface tension and to stabilize small air bubbles entrained into the concrete so that the ice formed within the pores is capable of expanding without breaking the structure of concrete.
In addition to the aforementioned gypsum, other augmenting retarders are also known in the art and are often used in massive monolithic casting operations where undue heat development is anticipated or in operations where concreting without the use of retarders may otherwise last longer, or when concrete is required to be transported for long periods of time.
Furthermore, several accelerating admixtures are known, which typically operate by containing anions that increase the solubility of lime in the mixing water, and thereby accelerate the autocatalytic effect of concrete setting caused by the presence of lime.
The aforementioned retarders utilized in this invention raise a high level of interest. They can be used for achieving effects which have not yet been intentionally and in a recognized manner used in concrete technology to a sufficient degree. The investigations performed by Banfill and Sauders (Cement and Concrete Research, 16, 1986, pp. 399 to 410) indicate that retarders have only a slight influence on heat development in hydration. Thus, the measured heat generation in the reference test was 3 mW/g maximally, while in conjunction with a sugar-retarded test it was 2.8 mW/g and with other retarders about 2.8 mW/g. The researchers came to the conclusion that the effect of retarders is not caused by inhibition of hydration via adsorption on the surface of cement particles.
Patent literature offers several examples of proposed solutions based on the use-of retarders. Thus, the WO patent application 82/000138 describes the use of retarders with controlled and repeatable action in mortars, into which up to 30% air is introduced with the admixing of retarders. The inventor has aimed to present "a method for controlled hydration of mortar by retarded initial setting". However, the presented aim seems to be in contradiction with the conclusions expressed by the researchers referred to above.
Equally, the U.S. Pat. publication No. 4,190,454 utilizes a retarder with a controlled retarding action in, for instance, a mix containing citric acid and soda, intended for use in a special cement which is otherwise immediately set after water mixing. Chemicals applicable in retardation and acceleration are also presented in the U.S. Pat. publication No. 3,619,221, which states that plasticizers, such as lignosulfonates, which are otherwise advantageous, almost invariably retard the hardening of concrete. According to the publication, the aforementioned retardation can be compensated by the addition of formic acid and water-soluble amine salts.
The objective of the U.S. Pat. publication No. 3,821,985 concerns admixtures applicable in retardation of cement mixes used in concretion of oil drilling holes. These extremely demanding objects which present a temperature of about 150.degree. C. and pressure exceeding 1000 bar, require a retarder of maximum conceivable efficiency.